The present invention relates to linear solenoid devices and, more particularly, to such a device in which the movable solenoid armature carries a plurality of permanent magnets which enable the device to provide a substantially higher force output than heretofore attainable.
A number of solenoid actuators in the past has incorporated permanent magnets, although such magnets have generally been configured and positioned within the solenoid devices to provide either detent or bidirectional capability. Devices in which one or more permanent magnets are incorporated within the stator structure of the solenoid device to hold the solenoid armature in one or more detent positions are disclosed in U.S. Pat. No. 4,072,918, issued Feb. 7, 1978, to Read; U.S. Pat. No. 3,886,507, issued May 27, 1975, to Johnston et al; U.S. Pat. No. 3,828,288, issued Aug. 6, 1974, to Boyd; U.S. Pat. No. 3,728,654, issued Apr. 17, 1973, to Tada; and U.S. Pat. No. 3,460,081, issued Aug. 5, 1969, to Tillman. Typically, the stator permanent magnet or magnets in such a device hold the armature in a detent position at one or both limits of armature movement with the actual movement of the armature to the detent positions being accomplished in a conventional manner. The magnets do not affect the force output of the solenoid device produced as the armature is moved toward the detent position or positions.
A number of other prior art patents disclose bidirectional solenoids in which the solenoid armature carries one or more permanent magnets, with the magnets on the armature being attracted or repelled to move the armature as desired in dependence upon the polarity of the current supplied to the stator coil of the device. This group of patents includes U.S. Pat. No. 4,065,739, issued Dec. 27, 1977, to Jaffe et al; U.S. Pat. No. 4,129,187, issued December 12, 1978, to Wengryn et al; U.S. Pat. No. 3,775,714, issued November 27, 1973, to Heuer; U.S. Pat. No. 3,914,723, issued Oct. 21, 1975, to Goodbar; U.S. Pat. No. 4,195,277, issued Mar. 25, 1980, to Leicht; and U.S. Pat. No. 3,202,886, issued Aug. 24, 1965, to Kramer. The Wengryn et al patent also incorporates a permanent magnet in the stator structure for repelling the armature in a first direction with movement of the armature in the opposite direction being provided as a result of energization of a stator coil which provides an opposing flux flow. The Jaffe et al patent discloses an armature arrangement in which the permanent magnet on the armature is radially polarized. Since the stator coil provides generally axial flux flow through the armature, apparently the lateral force of the armature results from nonuniformity of the flux density in the armature produced by energization of the stator coil. The Leicht patent discloses a device having a permanent magnet armature polarized in a direction normal to the direction of armature movement with a pair of oppositely polarized stator poles to effect simultaneous repulsion and attraction of the armature magnet.
U.S. Pat. No. 4,127,835, issued Nov. 28, 1978, to Knutson discloses a bidirectional solenoid device in which permanent magnets are mounted adjacent end plates at each end of the stator with a stator coil therebetween. The permanent magnets are oppositely polarized such that when the stator coil is energized, the flux produced by the coil adds to the flux produced by one of the magnets, while subtracting from or opposing the flux produced by the other of the magnets. Thus, one end of the armature is attracted more strongly toward its associated end plate than the other end of the armature.
U.S. Pat. No. 3,504,320, issued Mar. 31, 1970, to Engdahl et al, discloses a linearly acting current force transducer device having a pair of oppositely polarized permanent magnets mounted on the movable armature structure and including three separate serially connected stator coils. This arrangement is said to produce a high degree of linearity between the input current and the force output of the device.
Permanent magnets have also been incorporated into the rotor structure of rotary solenoid devices. Specifically, a variable reluctance rotary solenoid device including a pair of permanent magnets mounted on the rotor is disclosed in U.S. Pat. No. 4,135,138, issued Jan. 16, 1979, to McClintock. In the McClintock device, the rotor permanent magnets are repelled from the stator poles, as adjacent rotor pole surfaces are attracted toward the stator poles. McClintock, however, does not suggest utilizing such an arrangement in a linear solenoid device. Other rotary electromagnetic devices have incorporated a permanent magnet into the rotor structure, which magnet is simply attracted to one or more pole surfaces of a stator. Such devices are shown in U.S. Pat. No. 3,636,557, issued Jan. 18, 1972, to Watkins; U.S. Pat. No. 3,694,782, issued Sept. 26, 1972, to Ray; and U.S. Pat. No. 3,311,859, issued Mar. 28, 1967, to Bieger et al.
It is seen, therefore, that there is a need for a linear solenoid device which provides a substantially increased force output and which incorporates one or more permanent magnets into its armature.